This application is based on and claims priority under 35 U.S.C. xc2xa7 119 with respect to Japanese Application No. 2000-077092 on Mar. 17, 2000 and to Japanese Application No. 2001-076275 filed on Mar. 16, 2001.
The present invention generally relates to an actuator for an oscillator. More particularly, the present invention pertains to an actuator for an oscillator for oscillating electrostatic driven type oscillators provided with angular rate sensors.
A schematic illustration of related art actuators for an oscillator for oscillating electrostatic driven oscillators provided with an angular rate sensor is shown in FIG. 19. As shown in FIG. 19, a signal for the displacement of the electrostatic driven oscillator caused by the oscillation in a driving direction is outputted from a driving direction displacement detecting electrode 81 to a displacement signal detecting portion 82.
The displacement signal outputted to the displacement signal detecting portion 82 is synchronously detected at a timing synchronized to the displacement in a driving direction in a synchronous detection circuit 83 to be outputted to an amplitude adjuster 84 as oscillation amplitude data.
Simultaneously, the displacement signal outputted to the displacement signal detecting portion 82 is outputted to the amplitude adjuster 84 after being phase-shifted by approximately 90 degrees in a 90 degree phase shifter 85. By means of the phase shift of the displacement signal by approximately 90 degrees via the 90 degree phase shifter 85, an alternating voltage component of the drive signal having phase-contrast by approximately 90 degrees relative to the displacement signal is generated in the amplitude adjuster 84 to facilitate the oscillation of the electrostatic driven type oscillator.
The oscillation amplitude data outputted to the amplitude adjuster 84 is compared with a predetermined amplitude value in the amplitude adjuster 84. When the oscillation amplitude data is smaller than the predetermined amplitude value, an alternating voltage component of the drive signal having increased amplitude is generated (incremental adjustment). On the other hand, when the oscillation amplitude data is larger than the predetermined amplitude value, the alternating voltage component of the drive signal having decreased amplitude is generated (decremental adjustment). The amplitude adjustment of the alternating voltage component of the drive signal in the foregoing manner is performed for controlling the amplitude driving force of the oscillator to have constant amplitude in the driving direction of the oscillator. The alternating voltage component of the drive signal in which the amplitude is adjusted in the foregoing manner is outputted to an adder 86.
In the adder 86, a drive signal is generated by incorporating the alternating voltage component of the drive signal in which the amplitude is adjusted and the direct-current voltage component of the drive signal having a predetermined value. The drive signal generated in this manner is supplied to a drive electrode 87 fixed on a substrate. When the voltage of the drive electrode of the oscillator side is grounded (GND), the oscillator is oscillated to have constant amplitude in the driving direction by the oscillation of the electrostatic attraction generated to be proportional to the second power of the drive signal between the oscillator and the drive electrode 87.
Generally, electrostatic driven oscillators are oscillated by a drive signal consisting of the alternating voltage component and the direct-current voltage component supplied thereto. The electrostatic driven oscillators are oscillated by the oscillation of the electrostatic attraction generated proportional to the second power of the drive signal between the electrostatic driven oscillator and a drive electrode. The displacement of the electrostatic driven type oscillator according to the oscillation in a driving direction is detected as a displacement signal. The generation of the drive signal is controlled by an amplitude adjusting means to maintain the constancy of the oscillation amplitude of the electrostatic driven oscillator in a driving direction based on the detected displacement signal. By controlling the generation of the drive signal, the oscillation driving force of the electrostatic driven oscillator is controlled to maintain the constancy of the oscillation amplitude of the electrostatic driven oscillator in a driving direction.
The alternating voltage component of the drive signal is a cause of the noise of the displacement detecting signal because of the approximately same frequency with the displacement detecting signal. Thus, the alternating voltage component of the drive signal becomes a main cause of the detection error of the oscillation condition of the electrostatic driven oscillator. When an angular rate is detected during oscillation of the electrostatic driven oscillator applied to an angular rate sensor, the alternating voltage component causes a lag in the detected output.
When the amount of the noise derived from the alternating voltage component of the drive signal is stable, the detection error of the oscillation and the lag of the detected output of the angular rate maintain an approximately fixed level. When the detection error of the oscillation and the lag of the detected output of the angular rate maintain an approximately fixed level, they can be easily corrected. Therefore, when the amount of the noise derived from the alternating voltage component of the drive signal is stable, it is easy to correct the error. However, when the increase or decrease of the alternating voltage component of the drive signal is adjusted for maintaining the oscillation amplitude in a driving direction to be constant while the Q factor of the electrostatic driven oscillator in a driving direction fluctuates due to the change of the electrostatic driven oscillator due to the passage of time and the change in the environmental temperature, the amount of the noise mixed in the displacement detecting signal fluctuates. Thus, the detection error of the oscillation condition of the electrostatic driven type oscillator and the lag of the detected output of the angular rate are fluctuated by the increase or decrease of the alternating voltage component of the drive signal.
In order to minimize the fluctuation of the lag of the detecting output of the angular rate and the detection error of the oscillation condition of the electrostatic driven oscillator, it was proposed to control the oscillation drive force of the electrostatic driven oscillator to maintain the constancy of the oscillation amplitude of the electrostatic oscillator in a driving direction by increasing or decreasing only the direct-current voltage component while maintaining the constancy of the amplitude of the alternating voltage component of the drive signal.
Thus, as shown in a schematic illustration of FIG. 20, the displacement according to the oscillation of the electrostatic driven oscillator in a driven direction is outputted to a displacement signal detecting portion 92 from a driving direction displacement detecting electrode 91 as a displacement signal.
The displacement signal outputted to the displacement signal detecting portion 92 which is synchronously detected at a timing synchronized to the displacement in the driving direction in a synchronous detecting circuit 93 is outputted as the oscillation amplitude data to an oscillation adjuster 94. The oscillation amplitude data outputted to the amplitude adjuster 94 is compared to a predetermined amplitude value in the amplitude adjuster 94. When the oscillation amplitude data is smaller than the predetermined amplitude value, the direct-current voltage component of the drive signal is adjusted to be increased. On the other hand, when the oscillation amplitude data is larger than the predetermined amplitude value, the direct-current voltage component of the drive signal is decreased. The direct-current voltage component of the drive signal is adjusted to control the oscillation drive force of the electrostatic drive oscillator in order to maintain the constancy of the oscillation amplitude of the electrostatic drive oscillator in driving direction. The direct-current voltage component of the drive signal generated in the foregoing manner is outputted to the adder 95.
Simultaneously, part of the displacement signal outputted to the displacement signal detecting portion 92 is outputted to the alternating voltage component generating portion 97 after being phase-shifted by approximately 90 degrees via a 90 degree phase shifter 96. In the alternating voltage component generating portion 97, the alternating voltage component of the drive signal having the same frequency as the displacement signal, is phase-shifted approximately 90 degrees to the displacement signal, and having a constant amplitude is generated. The amplitude of the alternating voltage component of the drive signal is large enough to oscillate the oscillator at the resonant frequency. By shifting the phase of the alternating voltage component of the drive signal by approximately 90 degrees to the displacement signal, the oscillator can be driven at the most effective resonant frequency point which makes the oscillation of the oscillator easy. The alternating voltage component of the drive signal generated in the aforementioned manner is outputted to the adder 95.
In the adder 95, the adjusted direct-current voltage component Vdc of the drive signal and the alternating voltage component of the drive signal having the constant amplitude are added to generate an incorporated drive signal. The incorporated drive signal generated in the foregoing manner is supplied to the drive electrode 98. By the oscillation of the electrostatic attraction generated between the oscillator and the drive electrode 98 proportional to the second power of the drive signal, the oscillator is oscillated to maintain the constancy of the oscillation amplitude in the driving direction.
In the aforementioned actuator for an oscillator, in order to reduce the amount of the noise mixed in the displacement signal derived from the alternating voltage component of the drive signal, the alternating voltage component of the drive signal is predetermined to have a relatively small amplitude. However, in case the oscillation drive force of the oscillator is controlled only by the increase or decrease of the direct-current voltage component of the drive signal, a sufficient oscillation drive force cannot be obtained at the start at which the maximum drive force is needed compared to the force needed in a normal operation because the adjustment range of the direct-current voltage component is restricted by the capacity of the power supply voltage. Accordingly, it takes time to rise until the oscillation reaches a predetermined oscillation condition. This tendency is more remarkable in an oscillation having a higher Q-factor.
In light of the foregoing, it is an object of the present invention to provide an actuator for an oscillator to minimize unfavorable conditions such as the change of the detection error under the oscillation of an electrostatic driven oscillator.
It is a further object of the present invention to provide an actuator for an oscillator which is capable of shortening the rise time of the oscillation amplitude of an oscillator at the start.
To attain the above objects, the following technical means are provided with the actuator for an oscillator of the present invention which includes an oscillator driving means for oscillating an electrostatic driven oscillator by outputting a drive signal thereto, a displacement detecting means for detecting a displacement according to the oscillation of the electrostatic driven oscillator as a displacement signal, and an amplitude adjusting means for controlling the generation of the drive signal outputted from the oscillator driving means based on the detected displacement signal. The amplitude adjusting means comprises an alternating voltage component generating means for generating an alternating voltage component of the drive signal having a first amplitude in a normal operation and for generating the alternating voltage component of the drive signal having a second amplitude which is larger than the first amplitude at the start and a direct-current voltage component generating means for generating a direct current voltage component of the drive signal controlled to be increased or decreased based on the detected displacement signal. During the normal operation, the oscillation amplitude of the electrostatic driven oscillator is adjusted to be constant by controlling the oscillation force of the electrostatic driven oscillator based on an incorporated signal consisting of the direct-current voltage component and the alternating voltage component having a first amplitude. At the start, the oscillation amplitude of the electrostatic driven type oscillator is increased by providing a larger oscillation drive force to the electrostatic driven oscillator based on the incorporated drive signal consisting of the direct-current voltage component and the alternating voltage component having a second amplitude.
A second aspect of the technical means of the actuator for an oscillator of the present invention involves an alternating voltage component generating means comprised of an alternating voltage component generating portion for generating the alternating voltage component of a predetermined amplitude and an amplifying portion for generating the alternating voltage component of the drive signal having a first amplitude and the alternating voltage component of the drive signal having a second amplitude by amplifying the alternating voltage component of the predetermined amplitude by different amplification ratio in accordance with the distinction between a normal operation condition and a starting condition.
A third aspect of the technical means of the actuator for oscillator of the present invention involves an alternating voltage component generating means comprised of a first signal route for generating the alternating voltage component of the drire signal having a first amplitude, a second signal route for generating the alternating voltage component of the drive signal having a second amplitude, and a switching portion for switching the first signal route and the second signal route in accordance with the distinction of the normal operation condition and the starting condition.
A fourth aspect of the technical means of the actuator for oscillator of the present invention involves an oscillator driving means for oscillating the electrostatic driven oscillator by outputting a drive signal thereto, a displacement detecting means for detecting a displacement according to an oscillation of the electrostatic driven oscillator as a displacement signal, and an amplitude adjusting means for controlling the generation of the drive signal outputted from the oscillator driving means based on the detected displacement signal. The amplitude adjusting means is comprised of an alternating voltage component generating means for generating the alternating voltage component of the drive signal having a constant amplitude by phase-shifting and amplifying the displacement signal by a first amplification ratio at the normal operation and for generating the alternating voltage component of the drive signal by amplifying the displacement signal by a second amplification ratio which is larger than the first amplification ratio at a starting condition and is comprised of a direct-current voltage component generating means for generating the direct-current voltage component of the drive signal controlled to be increased or decreased based on the detected displacement signal. The oscillation amplitude of the electrostatic driven oscillator is adjusted to be constant by controlling the oscillation drive force of the electrostatic driven oscillator based on an incorporated signal consisting of the direct-current voltage component and the alternating voltage component having a constant amplitude amplified by the first amplification ratio at the normal operation. The oscillation amplitude of the electrostatic driven oscillator is increased by driving the larger oscillation drive force relative to the electrostatic driven oscillator based on an incorporated drive signal consisting of the direct-current voltage component and the alternating voltage component amplified by the second amplification ratio at the start.
A fifth aspect of the technical means of the actuator for an oscillator of the present invention involves the normal operation condition and the starting condition being distinguished by the passage of time after the start.
A sixth aspect of the technical means of the actuator for an oscillator of the present invention involves the normal operation condition and the starting condition being distinguished by the comparison between a predetermined amplitude at a start condition and the oscillation amplitude of the electrostatic driven oscillator detected based on the displacement signal.
A seventh aspect of the technical means of the actuator for an oscillator of the present invention involves the normal operation condition and the starting condition being distinguished by the comparison between the direct-current voltage component and a predetermined voltage at the start condition. The oscillation amplitude is set to be proportional to the oscillation frequency.
According to the first through the fourth aspects of the technical means, the oscillation adjusting means generates the incorporated drive signal consisting of the direct-current voltage component controlled to be increased or decreased based on the detected displacement signal and the alternating voltage component having a first amplitude by the alternating voltage component generating means and a direct-current voltage component generating means at the normal condition. Based on the incorporated drive signal, the oscillation drive force of the electrostatic driven oscillator is controlled to maintain the constancy of the oscillation amplitude of the electrostatic driven oscillator in driving direction. Thus, even when the Q factor of the electrostatic driven oscillator in a driving direction fluctuates due to the change of the electrostatic driven oscillator by the passage of time and the change of the environment temperature, only the direct-current voltage component of the drive signal is increased and decreased to maintain the constancy of the alternating voltage component (amplitude). Accordingly, even when the Q factor of the electrostatic driven oscillator in a driving direction fluctuates due to the passage of time and the change of the environment temperature, the amount of the noise in the displacement signal deriving from the alternating voltage component of the drive signal is kept stable. This helps the correction of detection error changes as long as the noise amount is stable by keeping the fixed level.
On the other hand, the oscillation adjusting means generates the incorporated drive signal consisting of the direct-current voltage component controlled to be increased or decreased based on the detected displacement signal and the alternating voltage component having the second amplitude which is larger than the first amplitude by the direct-current voltage component generating means and the alternating voltage component generating means at the start. Based on the incorporated drive signal, the oscillation amplitude of the electrostatic driven type oscillator is increased by driving the larger oscillation drive force relative to the electrostatic driven oscillator. Accordingly, the rise time of the oscillation amplitude of the electrostatic driven oscillator at the start is shortened.
Particularly, according to the fourth aspect of the technical means of the present invention, the alternating voltage component of the drive signal is generated only by phase-shifting and amplifying the displacement signal irrespective of the normal operation condition or the starting condition. When the oscillation amplitude of the electrostatic driven oscillator is kept stable, the alternating voltage component of the drive signal having the constant amplitude is generated only by phase-shifting and amplifying the displacement signal based on the oscillation of the electrostatic driven oscillator. Accordingly, the circuit structure of the alternating voltage component generating means is simplified compared to generating the alternating voltage component of the drive signal separately.
According to the fifth aspect of the technical means of the present invention, the distinction between the normal operation condition and the starting condition can be performed with simpler circuit structure based on the passage of time after the start.
According to the sixth aspect of the technical means of the present invention, the distinction between the normal operation condition and the starting condition can be performed more precisely by comparing the predetermined amplitude at the start and the oscillation amplitude which shows the actual oscillation condition of the electrostatic driven oscillator.
According to the seventh aspect of the technical means of the present invention, the distinction between the normal operation condition and the starting condition can be performed with a simpler structure and more precisely by comparing the direct current voltage component and the predetermined voltage at the start.